Featured Scientist: Michael Landry

As we wrap up this year's survey, the first of two annual research surveys in the Gulf of Mexico for the NOAA RESTORE Act Science Program, we'd like you to get to know the PI from Scripps Institution of Oceanography, Professor Mike Landry! Read on as he describes his research and our cruise goals in his own words!

"I am a biological oceanographer. I have been on many ocean research expeditions over the years (since the 1970s), but never on a cruise in the Gulf of Mexico, never on a NOAA ship and never with fisheries scientists trying to understand a specific fisheries-related problem. So this particular cruise is special and a new learning experience in many respects. At the same time, it is also familiar. What we have investigated on past expeditions is how plankton food webs in different areas of the oceans function under different environmental conditions in order to understand the “rules” of why systems vary and how they respond to change. Our hope in this project is to apply the techniques that we have developed and the results from past experiences to characterize the unique aspects of the Gulf of Mexico habitat that lead to rapid growth and success of larval bluefin tuna (why do momma tunas migrate vast distances to spawn in only few small places in the ocean?) so that fisheries scientists might be better able to predict how they might be affected by future ocean changes.

Above: Groups of water bottles to
be sent to different depths
Below: Our filtration set up -
6 bottles at once!

"In this project, we are taking two approaches to studying food-web relationship and rates. One is experimental, involving direct measurements of community composition, productivity and nutrient uptake by phytoplankton, the microscopic plants of the sea. We also measure the consumption (grazing) of phytoplankton by zooplankton, the slightly larger but still pretty small protozoa and small animals that comprise the first 2-3 steps of the ocean food web. This is the “what is there,” "what are they doing,” and “how fast are they doing it” part of the study. Phytoplankton often go through one or two generations (cell divisions) per day, and they get eaten almost as fast as as they divide, so the tricky part of these experiments is separating the two rates (production growth and grazing loss) that are going on at the same time. We have a technique for this, which involves dilution of the grazing impact (using filtered water, changing the encounter frequency of predators and prey) in some of our experimental bottles. It is also important that we run our experiments under natural conditions of underwater light and temperature, so all of our experimental bottles that contain the plankton that we collected at different depths are put in net bags and attached at same depth to a line underneath a free-floating drifter float that we track by satellite for a day before picking up and exchanging bottles for a new batch of experiments. After a lot of filtering, preservation or freezing, and later analysis in our lab on shore, we should have a pretty good picture of how productivity and nutrients are moving through various routes in the food web to get to the specific zooplankton prey that bluefin tuna larvae like to eat.

Tom (L) and Mike (R) attach bottles to the sediment trap array

Mike (L) and Aki (R) hunt for BFT using microscopes onboard

"In the second approach to this study, we will use the tuna larvae themselves to tell us where they reside in the food web and what is the main source of nutrients (nitrogen) for primary production. This information resides in the nitrogen isotopic composition of the amino acids that make up the proteins of the tuna larva muscle tissue, which varies with the source of nitrogen (N2 gas for nitrogen fixation versus nitrate from deep water upwelling) and the number of predator-prey steps that the nitrogen has taken to get to the larvae, starting from phytoplankton. This sounds complicated, but the isotope analysis is easier to do than all of the experiments that are needed to assemble the food-web picture. One of our goals is to see if results from these two approaches agree, which has never been done before for any system because the isotope approach is so new. If this works out, it would validate using the isotopes in future studies, or also to look at changes in food-web structure and nitrogen sources that may have already occurred with climate change, using the muscle tissues of fish samples that have been taken in the past and preserved in museum collections."

Featured Scientist: Tom Kelly

Today we learn about Tom who shares his insights into the infamous sediment trap! Here is his blog post. (Read previous guest posts here!)

Tom and the incubation system

My name is Thomas Kelly and I am a PhD Candidate at Florida State University in the Plankton Ecology and Biogeochemistry Lab. One of the principal tools that I use in my research is called a sediment trap. A sediment trap collects marine particles and organisms as they sink through the water column. You can think of a sediment trap as an underwater rain gauge that collects sinking plankton instead of falling rain drops.

Since most of the biological growth occurs where light is plentiful (i.e. photosynthesis), the majority of marine organisms live within the surface layers of the oceans. But as these organisms die, get broken up, or defecate, particles settle out of the surface layer and into the deeper ocean. Our sediment traps are placed in between these layers and can tell us about what kind and how quickly carbon, nutrients, and other material leaves the surface ecosystem.

Tom and Mike deploy the sediment trap

The deployment of the sediment trap is really quite straightforward and will typically take a bit over an hour. The whole assembly consists of a long rope that extends from the surface all the way down to the depth of the last sediment trap frame (Pictured to the left), about 650 (210m) feet. At the bottom we place 60 lbs (27 kg) of weights and at the top a set of buoys. For the Bluefin Tuna Cruise the sediment trap frames are placed at approximately 150, 400, and 600ft (50, 120, and 200m) of water depth so that we can measure how the sinking of particles changes with depth.

Onto the frame we attach a set of tubes filled with extra salty seawater so that any particles that sink into them will stay in the tube rather than being mixed out again (the denser fluid will stay inside the tube just like a glass of water will stay inside a cup). Besides that, the tubes are also spiked with formaldehyde to kill anything that tries to eat the sinking material and a baffle at the top to reduce turbulence around the top of the tube.

Tom plots his next filtration experiment

After 3-5 days of drifting, the sediment trap is ready to come aboard and be processed. In general, each of the sampling tubes is filtered and frozen for later processing on land where we can look at such things as the carbon and nitrogen content. Some of the specialized aspects that we can look at from the sediment traps include the size classes of the particles collected, the source of the material collected, and the quantity of various metals and nutrients within the material. Ultimately the sediment trap provides invaluable information about how the ecosystem looses energy and material to the deeper water column.